In U.S. Pat. Nos. 6,869,206, 6,960,872, 7,025,464, 7,040,774, and 7,048,385, a means of generating a high brightness light source uses light emitting diodes in a light recycling cavity. This present invention relates to an improved method and process for fabricating an integrated light recycling cavity, color combiner, optical collimator, and heatsink. In U.S. Pat. No. 7,040,774, a light recycling cavity contains different colored LEDs within the cavity. That light recycling cavity permits multiple LEDs of different colors to mix their outputs within the cavity. This multiple and mixed outputs can be very efficient in that the étendue of the light source is defined by the exit aperture of the light recycling cavity and not by the cumulative area of the LEDs within the cavity.
In conventional light engines used for projection displays, a white light source, such as an arc lamp, must be broken up into multiple colors to generate a full color display. This white light source is very inefficient. For example, a color separation system using a color wheel of alternating red, green, and blue filters can maximally only be 33% efficient. For a light engine using separate distinct colored sources, the sources must be combined onto the same optical path using dichroic mirrors, which can also be inefficient.
Light sources for microscopes, endoscopes, fiber optic illuminators, spotlights, and down lighting for general illumination all have a need for a tunable color temperature (e.g. being able to select the mix of red, green and blue or other color) projected. Space and volume is at a premium for optical systems that are very compact, such as pocket projectors. With conventional light sources, a relatively long optical train is required to collimate and integrate the colors into the projection engine.
Adding to the overall size are the heatsinks required to dissipate the heat from the light source. These heatsinks add volume, which must be accommodated within a compact optical system.
LEDs typically emit in a Lambertian full solid angle. To efficiently couple this light into an optical system requires collecting this wide angle light and collimating it. This collection and collimation is typically done with an optical tunnel or taper. The optical tunnel consists of four mirrored surfaces, which form a tunnel. Alternatively, a solid glass tapered rod may be used. The output aperture of the tunnel is larger than the input of the tunnel to collimate the light. The length of the tunnel must necessarily be made long to provide homogenization of the light that enters the tunnel. 40 mm to 80 mm is typical for the length of these tunnels. Thus, the tunnel not only collimates the light, it also aids in making the light more uniform.
In the prior art, these optical tunnels are appended to the output of LEDs where the LEDs are mounted on their own heatsink, the heatsink protruding in the opposite direction of the tunnel. The combination of the heatsink and the optical tunnel add considerably to the overall size of the finished light source.
Minimizing the manufacturing cost is paramount in consumer products, such as projectors, televisions, etc. Optical tunnels and heatsinks can add substantially to the cost of the finished product.
There is a need for a light source for these various applications that is compact, inexpensive, and well collimated and can be tuned to different color temperatures or different colors depending on the application, mood, or environment.